The present invention relates to space transformer configurations of chip testing probe apparatus. Particularly, the present invention relates to a probe apparatus having a segmented space transformer.
The demand for reduced test cycle times during the chip fabrication results in development of probe apparatus that are capable of testing an increasing number of chips simultaneously. Chips are conventionally fabricated and tested on wavers. For a given chip size, the waver diameter defines the maximum number of chips that can be simultaneously fabricated on a single waver. On the other hand, the maximum number of simultaneously tested chips is mainly restricted by the configuration of the probe apparatus.
Conventional probe apparatus have a number of probes configured and uniformly assembled in order to evenly contact a number of chip terminals. The maximum number of probes feasibly combined in such probe apparatus depends on a number of factors, which are, for example, a probe failure likelihood opposed by a required probe apparatus life span or, in another example, position tolerances of all the probes"" tips within the probe assembly.
Probe failure likelihood may be statistically defined as an average failure rate per probe and test cycle. Multiplying the number of assembled probes with the average failure rate results in an average probe apparatus cycle interval during which the probe apparatus may be operated uninterrupted. The repair of individual probes within a conventional probe assembly is highly unpractical due to the fragile nature of probes and the tight probe assembly. In cases where individual probe tips become offset relative to the probe tip plane, grinding and/or sanding operations have to be performed on all probes in order to bring them again into common alignment. Thus increasing the number of probes increases also the maintenance and repair effort between the cycle intervals.
Position tolerances of all the probe tips within the probe assembly are crucial for establishing and maintaining identical contacting conditions between the individual probe tips and the terminals of the tested chips. In-plane position tolerances affect the position of the probe tips relative to the corresponding terminals. Off-plane position tolerances affect the contacting force with which the probes are pressed against the terminals. In-plane and off-plane position tolerances are defined by a fabrication precision and a thermal expansion behavior of the probe apparatus. Since chips are tested at various elevated temperatures, probe apparatus are exposed to varying thermal conditions during their operation. With increasing size of the probe apparatus temperature discrepancies within the probe apparatus become more difficult to control. In addition, individual components of the probe apparatus have dissimilar expansion characteristics, which results in warping and consequently in an increased off-plane position range of the probe tips.
Space transformers that are made from two or more layers of different materials are especially sensitive to warping. Warping of space transformers increases more than proportional with the size of space transformer and is thus a main limitation of probe apparatus sizes for given probe tip position tolerances.
For simultaneously testing extended numbers of chips, there exists therefore a need for a probe apparatus in a configuration that bypasses the limitations imposed by probe failure likelihood and space transformer warping. The present invention addresses this need.
The U.S. Pat. No. 5,534,784, for example, discloses a probe apparatus having more than one space transformers on top of each other. The invention does not disclose laterally arranged space transformer segments.
A probe apparatus is introduced that combines a number of laterally arranged probe blocks in a modular assembly within a frame structure.
In the preferred embodiment, the probe blocks include space transformer segments that are configured, laterally arrayed and fixated within the frame structure such that the off-plane position range of the probe tips remains only affected by the warping of the individual space transformer segments. In addition, the frame structure may have thermal distribution characteristic defined such that temperature discrepancies of the individual space transformer segments remain within a predetermined range for a given operation environment.
In a second embodiment of the present invention the probe modules include space transformer segments, corresponding probes and a guiding structure for glidingly fixating the corresponding probes. The frame structure may provide features for fixating and removing the probe modules in order to replace individual probe modules within the probe apparatus in cases of probe failure or other factors like, for example, partial change of the chip layout of the waiver series to be tested. As a result, the number of probes within the probe apparatus may be selected independently from the average probe failure likelihood and the probe apparatus may be more easily configured and adjusted to varying chip production cycles.